Illumination systems are known per se. They are used, inter alia, in luminaires for general lighting purposes, for example, for office lights, shop lights or, for example, shop window lights. Alternatively these illumination systems may be used for illuminating advertising boards, for example, advertising boards illuminating a partially transparent image from the back of the image.
The known illumination systems may also be used as light sources in backlighting systems in (picture) display devices, for example, for TV sets and monitors. Such illumination systems are particularly suitable for use as backlighting systems for non-emissive displays such as liquid crystal display devices, also denoted as LCD panels, which are used in (portable) computers or (portable) telephones.
Organic light emitting diode devices (further also indicated as OLED devices) are in many ways considered as the future in various lighting applications. They may, for instance, be used to create ambient lighting which is emitted from relatively large light emitting surfaces. In addition to high efficiency, such large area light emitters also provide interesting design possibilities to design general lighting systems. A drawback of such OLED devices is that the angular distribution of the light emitted from a light emitting surface of the OLED device is substantially Lambertian, which may cause glare when used in general lighting systems. Glare results from excessive contrast between bright and dark areas in the field of view. Glare can, for example, result from directly viewing a filament of an unshielded or badly shielded light source. To prevent glare, a normalized emission profile is defined in, for example, the European Standard EN12464-1 which dictates that the emission of light should be cut off at emission angles exceeding 60 degrees when the lamp luminance exceeds 500 kcd/m2. Similar standards apply in other regions. Since the OLED device has a relatively large light emitting surface from which light is emitted having a substantially Lambertian emission distribution, the shaping of the emitted light to comply with the normalized emission profile while maintaining a relatively high efficiency is relatively difficult.